A Study On Electrochemical Sensor For Ammonia

In order to overcome electrolyte dryout problem in the traditional ammonia gas sensor,extensivly study were made on ammonia oxidation in various organic solvent. It was found that the ammonia oxidation is easier in the mixtures of organic solvent (DMF)and the room temperature ionic liquid(RTIL)than in DMF.An ammonia sensor,which employs propylene carbonate as electrolyte,and Pt/Ir nanoparticles as catalyst,can rapidly response the change of the concentration of ammonia.On the other hand,ammonia largely dissolves in water,and transforms into NH₄⁺ ion,which is electrochemical inactive.It is necessary to detect the NH₄⁺ concentration in water. Cu/carbon nanotube(MWCNT)material was used for detection NH₄⁺ in water.The main points of this thesis are expressed as follows:1.Ammonia direct electrochemical oxidation in organic solvent of THF,AT,FM, DMF,DMSO with LiClO₄ as electrolyte.The ammonia electrochemical oxidation happened in the above five organic solvents,the ammonia oxidating peak partly overlap with the organic solvent own oxidation peak.The ammonia- oxidating peak is very wide in THF,with low peak current.In AT,FM and DMSO,the ammonia oxidating peak majority overlaps solvent oxidating peak,does not favor the ammonia oxidating current examination.Only in DMF,the ammonia oxidating peak current is relatively well distinguished(appears in 1.2 V vs Ag).But this time DMF already inevitable occur oxidation;disturbing ammonia oxidized current examination. However,when joins the ionic liquid to DMF([bmim]BF₄),the oxidation current of DMF would be inhibited,the oxidation peak of NH₃ would shift negatively from 1.2 V to 0.90 V simultaneously.The DMF- RTIL([bmim]BF4)system suggests new method for gas sensor electrolyte development.2.The direct electrochemical oxidation of ammonia in propylene carbonate (containing 0.1 mol/L TBAP),using Pt,Ir,Pt/Ir black as catalyst,which are being modified to GC electrode.On the Ir black catalyst the oxidation of ammonia(200 ppm)began at 0.4 V,and the oxidation current density attaining to the maximum of 45μA/cm² at the voltage of 1.0 V.On the Pt black,the oxidation behavior was not observed because of the structure of prepared Pt black.While Pt/Ir(1:1)black showed great activity for the electrochemical oxidation of ammonia,began at 0.2 V and the current density attaining to the maximum of 100μA/cm².Cuurrent-tirne curve show that Pt/Ir (1:1)black attain to stabilized currrent density,which is in good linear-ship with ammonia concentration,according to various ammonia concentration(50-200 ppm) in few seconds.It was indicted that Pt/Ir(1:1)based sensor has the virtues of amperemeteric ammonia gas sensor.Since the propylene carbonate has low evorpation,the prepared sensor may expand its life span compared with the traditional water based sensor.3.Canbon nanotube(CNT)/copper was modified to GC electrode,in carbon buffer(50 mmol/L,pH =10),spiking different ammonium directly into water,by Differential Pulse Voltammetry method,the reduce peak current increasing with concentration of ammonium,and keep in linear range of concentration(20-100μmol/L).This is new method of detection NH₄⁺ in water.